This invention relates to a fuel processor and method for reforming natural gas and other hydrocarbon fuels to produce a reformed fuel suitable for direct use in an electrochemical fuel cell. More particularly, this invention relates to a fuel processor and method whereby natural gas or other hydrocarbon fuels are first subjected to the well-known reforming reactions in which the fuel is reacted with steam, resulting in the formation of a reformer effluent comprising hydrogen, carbon dioxide and a substantial amount of carbon monoxide. To reduce the amount of carbon monoxide, the reformer effluent is subjected to a shift reaction in which the carbon monoxide reacts with steam to provide carbon dioxide and additional hydrogen. Although the shift reaction substantially reduces the carbon monoxide present in the effluent, it is still too high for use in fuel cells such as polymer electrolyte membrane (PEM) fuel cells. Subsequent methanation in accordance with the method of this invention results in a mixture of gases comprising hydrogen, carbon dioxide and gaseous water, but little or no carbon monoxide. The hydrogen recovered from the mixture is of sufficient purity to enable its use in a PEM fuel cell. The fuel processor of this invention can also be used to supply hydrogen for a hydrogen refueling station.
Developers worldwide are currently working on numerous schemes for converting fuels. Within the fuel processor, much work has been focused on carbon monoxide control using selective catalysts that preferentially oxidize the carbon monoxide in the hydrogen-rich processed gas. However, for several reasons, this method is less than ideal. Firstly, the catalysts employed by such schemes are not 100% carbon monoxide selective. Secondly, significant combustion heat is evolved from consuming both carbon monoxide and hydrogen gases, thereby requiring the use of two or three stages coupled with heat exchanger equipment and controls for metering air bleeding. Thirdly, the air has to be metered in proportion to the amount and duration of the carbon monoxide content. And, fourthly, these systems are expensive to build and there is at present no accurate, real-time carbon monoxide sensor suitable for use in this system, as a result of which, in transient states, excess hydrogen is combusted to assure all of the carbon monoxide is consumed.